1. Field of the Invention
This invention relates generally to analytical instruments, and more particularly to instruments which include the combination of a gas chromatograph and a mass spectrometer.
2. Description of the Related Art
A gas chromatograph (GC) is an analytical instrument which can separate a gaseous mixture into its various constituent parts. A mass spectrometer (MS) is an analytical instrument which can analyze a gaseous sample to determine its molecular structure. When the output of a gas chromatograph is coupled to the input of a mass spectrometer, the combination instrument is known as a gas chromatograph/mass spectrometer (GC/MS).
Both gas chromatographs and mass spectrometers have been around for a relatively long period of time. However, combination GC/MS instruments are relatively recent innovations, and continuing research and development is directed towards improving the interface between the gas chromatograph and the mass spectrometer portions of GC/MS instruments.
A typical GC/MS interface includes a tubular transfer line having one end coupled to the output of the gas chromatograph and having its other end extending into a vacuum chamber of the mass spectrometer. An ion source of the mass spectrometer is used to ionize the effluent from the transfer line, and a quadrupole filter of the mass spectrometer is used to filter the ionized components of the gas according to mass. An ion detector within the vacuum chamber of the mass spectrometer detects ions filtered through the quadrupole filter. Finally, the recorded output signal of the detector is studied to determine the chemical structure of the gas sample.
A problem with prior art GC/MS interfaces is the complexity and cost of the associated heating systems. In a GC/MS instrument, the interface should be kept very hot to maintain the temperature of the gaseous sample flowing from gas chromatograph. Within the mass spectrometer, the ion source should be hot, the quadrupole should be moderately hot, and the ion detector should be at, or slightly above, ambient temperature.
In the past, this range of temperatures has been accomplished by providing separate heaters for the interface, ion source, and quadrupole. In consequence, prior art GC/MS instruments have a complex assemblage of heaters and associated controllers, each of which adds to the cost and complexity, and reduces the reliability, of the instrument. These problems were compounded by the fact that two of the three heaters (i.e. the heaters for the ion source and the quadrupole) were internal to the vacuum system of the mass spectrometer, and were therefore difficult to access for adjustment, repair, or replacement.